Cement-containing catalyst composition and process for its preparation

ABSTRACT

A solid composition is prepared by mixing water, a hydraulic cement, sodium silicate, and a catalyst composition comprising (a) an inorganic support, (b) Pt and/or Pd metal and (c) Fe metal and/or oxide, followed by maintaining the obtained mixture under such conditions as to affect hardening of the hydraulic cement. Preferably, the hydraulic cement is a Type III portland cement and/or a Class H well cement. A solid composition comprising hydraulic cement, sodium silicate and the above-described catalyst composition is provided. This solid composition can be used as a CO oxidation catalyst.

BACKGROUND OF THE INVENTION

In one aspect, this invention relates to a process for preparing a cement-containing composition. In another aspect, this invention relates to a cement-containing composition which is active as a CO oxidation catalyst.

The use of catalysts for the oxidation of carbon monoxide to carbon dioxide by reaction with oxygen, in particular at low temperature, is of much interest, e.g., in CO₂ lasers for combining CO and O₂ formed by dissociation of CO₂ during discharge. In the latter application, the presence of O₂ is most undesirable because it can cause a breakdown of the electrical field in the laser cavity. Several patents, such as U.S. Pat. Nos. 4,818,745; 4,902,660; 4,920,088 and 4,921,830 disclose compositions useful as CO oxidation catalysts in CO₂ laser applications. However, there is an ever present need to develop new, effective CO oxidation catalyst compositions having high particle strength and high abrasion resistance, and to develop improved processes for preparing effective CO oxidation catalyst compositions.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a cement-containing composition which is effective as a catalyst for converting carbon monoxide and free oxygen to carbon dioxide. It is another object of this invention to provide a process for preparing a cement-containing catalyst composition. Other objects and advantages will be apparent from the detailed description and the appended claims.

In accordance with this invention, a solid composition of matter comprises a mixture of

(1) a hardened hydraulic cement,

(2) sodium silicate, and

(3) a catalyst composition comprising (preferably consisting essentially of)

(a) an inorganic support material, preferably at least one of alumina, magnesia, magnesium aluminate (MgAl₂ O₄), hydrotalcite, silica, titania, zirconia, vanadia and combinations thereof,

(b) at least one of platinum and palladium metal, and

(c) at least one iron component selected from iron oxide, iron metal and mixtures thereof.

In a preferred embodiment, the inorganic support material of the catalyst composition is titania. In another preferred embodiment, the noble metal component (b) of the catalyst composition is platinum.

In a further preferred embodiment, the hydraulic cement is a Type III portland cement, as defined in ASTM Method C 150-86 (1988 Annual Book of ASTM Standards, Section 4, Volume 04.01, pages 116-120).

In a still further preferred embodiment, the hydraulic cement is a Class H well cement, as defined in API Specification 10, entitled "Specification for Materials and Testing for Well Cements", Aug. 1, 1988, American Petroleum Institute.

In still another embodiment, the composition of matter of this invention is active as catalyst for the oxidation of CO with O₂ to CO₂, at about 15°-50° C.

Also, in accordance with this invention, a process for preparing a solid composition of matter comprises the steps of:

(A) mixing water, a hydraulic cement, sodium silicate, and a catalyst composition comprising components (a), (b) and (c), as defined above; and

(B) maintaining the mixture obtained in step (A) under such conditions so as to affect hardening (setting) of the hydraulic cement, and to substantially dry the mixture of step (A) so as to obtain a substantially dry, solid composition of matter (preferably being active as a catalyst for the conversion of carbon monoxide and oxygen to carbon dioxide at about 10°-50° C.).

Preferred are TiO₂ as component (a), Pt as component (b), and Type III portland cement (defined above) and/or Type H well cement (defined above) as the hydraulic cement.

DETAILED DESCRIPTION OF THE INVENTION

Any suitable, effective inorganic support material can be used as component (a) of the catalyst composition, which is compounded with a hydraulic cement and sodium silicate. Preferred inorganic support materials are alumina, magnesia, magnesium aluminate (MgAl₂ O₄), hydrotalcite (described in U.S. Pat. No. 4,902,660), preferably Mg₄.5 Al₂ (OH)₁₃ CO₃.3.5 H₂ O), silica, titania, zirconia, vanadia (in particular V₂ O₅) and mixtures thereof. Titania (described in U.S. Pat. No. 4,920,088) is particularly preferred. Generally the surface area (determined by the BET/N₂ method; ASTM D3037) of the inorganic support material is in the range of from about 10 to about 300 m² /g. The support material particles can have any suitable shape, such as spherical, trilobal, quadrilobal, cylindrical, irregular (granular) and the like.

Component (b) of the catalyst composition (compounded with a hydraulic cement and sodium silicate) is Pt or Pd or a mixture of both noble metals, preferably Pt; while the iron component (c) preferably is substantially iron oxide. Generally, the catalyst composition contains about 0.05-10 weight-% Pt or Pd or (Pt+Pd) and about 0.1-15 weight-% Fe. The preparation of the catalyst composition comprising components (a), (b) and (c) has been described in the U.S. patents cited above in the section entitled "Background of the Invention" and need not be described herein. The last step in the preparation is a reducing treatment with a reducing gas, in particular CO or H₂ or mixtures thereof. The reducing conditions have been described for the various catalyst compositions in the U.S. patents cited above, and preferably comprise a reducing temperature of about 0°-500° C., more preferably with H₂.

Any of the well known hydraulic cements can be used in making the composition of matter of this invention. A description of suitable hydraulic cements is contained in Kirk-Othmer "Encyclopedia of Chemical Technology", Third Edition, Volume 5, John Wiley and Sons, 1979, pages 163-193. Particuarly preferred are portland cements which contain CaO, Al₂ O₃ and SiO₂ in various combinations, phases and proportions such as Type I, IA, II, IIA, III, IIIA, IV and V portland cements, as defined in ASTM Method C 150-86 (1988 Annual Book of ASTM Standards, Section 4, Volume 04.01, pages 116-120). Particularly preferred is a Type III portland cement which typically contains about 60-65 weight-% CaO, about 20-22 weight-% SiO₂, about 4-6 weight-% Al₂ O₃, about 2-3 weight-% Fe₂ O₃, about 1-3 weight-% MgO and about 2-3 weight-% SO₃ (as sulfate).

Other preferred hydraulic cements are specific portland cements which are used for cementing steel casings of gas and oil wells to the walls of the bore hold and to seal the porous rock formations. These well cements include Class A, B, C, D, E, F, G, H, and J well cements, as defined in API Specification 10, Fourth Edition, Aug. 1, 1988, entitled "Specification for Material and Testing for Well Cements", of the American Petroleum Institute 1120 L. Street NW, Wasington, D.C. 20005. Particularly preferred is a Type H well cement which contains about 48-65 weight-% tricalcium silicate (3CaO--SiO₂) as the major component, and additionally various amounts of tricalcium aluminate (3CaO.Al₂ O₃), tetracalcium aluminum ferrite (4CaO.Al₂ O₃ Fe₂ O₃), sulfates of Mg and/or Ca. It is within the scope of this invention to employ a mixture of Type III portland cement and Class H well cement (at any suitable weight ratio, such as 1:100 to about 100:1).

Any water-soluble sodium silicate, such as those described in Kirk-Othmer's "Encyclopedia of Chemical Technology", Volume 20, John Wiley and Sons, Inc., 1982 pages 855-876, including orthosilicate, pyrosilicate, metasilicate, polysilicate), can be employed as component (2) in the process of this invention. Preferred sodium silicates are those contained in water glass. Presently most preferred is sodium metasilicate, (Na₂ SiO₃)_(n), with n being 4-6. Generally the mole ratio of SiO₂ to Na₂ O in the sodium silicate is in the range of from about 1:1 to about 4:1.

Any suitable method of mixing the hydraulic cement, sodium silicate, the catalyst composition containing components (a), (b) and (c), and water can be employed. Generally dry powders of cement, sodium silicate and catalyst composition are dry-blended, and thereafter water is added with stirring. However, it is also feasible to employ an aqueous solution of a sodium silicate, such as water glass (a commercially available inorganic binder or glue) in lieu of solid sodium silicate.

Any suitable weight ratio of the various components can be employed during the mixing step. Generally, the weight ratio of hydraulic cement to catalyst composition is in the range of from about 0.1:1 to about 10:1, preferably about 0.5:1 to about 3:1; and the weight ratio of hydraulic cement to sodium silicate (on a water-free basis) is in the range of from about 2:1 to about 200:1, preferably about 10:1 about 50:1; and the weight ratio of hydraulic cement to water is in the range of from about 0.1:1 about 20:1, preferably about 0.5:1 to about 4:1.

The thorough mixture of the hydraulic cement, sodium silicate, the catalyst composition and water is then maintained at about 20°-30° C. (room temperature) or, preferably at an elevated temperature (such as 30°-100° C.) for a sufficient time to cause the hydraulic cement to harden, which may require about 0.5 to about 30 hours (depending on the temperature). Simultaneously with the hardening process, or after the hardening process is substantially complete, excess water (i.e., water not bound in the hardening of the cement) is removed from the mixture. Finally, there is obtained a solid, hardened composition comprising (A) hardened hydraulic cement, (B) sodium silicate and (C) the catalyst composition comprising components (a), (b) and (c), with a water content of less than about 2 weight-%, preferably less than 1 weight-% H₂ O. The hardening process can be carried out in a mold so as to give the hardened composition a desired shape (e.g., one to fit a CO₂ laser cavity into which the composition of this invention is placed for catalyzing the recombination of CO and O₂ to CO₂). Preferably, the hardened composition is treated with a reducing gas, such as free hydrogen (preferred) or carbon monoxide, preferably for about 0.5-5 hours at about 100°-300° C.; in particular when the hardened composition is to be used as a catalyst for the oxidation of CO with O₂ to CO₂.

The solid, hardened composition of matter of this invention can be used as catalytic composition for various reactions, such as oxidation of CO with O₂ to CO₂, or oxidation of N₂ O or NO with O₂ to NO₂, or oxidation of hydrocarbons (e.g., those contained in the exhaust gases of automobile engines) with O₂ to CO₂ and H₂ O, and the like. The presence of the hydraulic cement in the composition of matter of this invention will impart high particle strength and high abrasion resistance, which are desirable properties (especially when "dusting" of the composition is to be avoided, e.g., in laser applications). Preferably, the composition of matter is used in a process for oxidizing CO with free oxygen to CO₂, especially in CO₂ lasers.

The process conditions for oxidizing a carbon monoxide containing feed gas are well known and have been described in the U.S. patents cited in the "Background of the Invention" section. The reaction temperature generally is in the range of from about -50 ° to about 400° C., preferably from about -30° to about 170° C., more preferably from about 10° to about 50° C. The pressure during the oxidation process generally is in the range of from about 1 to about 2,000 psia, more perferably from about 5 to about 20 psia. The volume ratio of CO to O₂ in the feed gas range from about 1:100 to about 100:1, and preferably is in the range of about 1:10 to about 10:1. The volume percentage of CO and the volume percentage of O₂ in the feed gas can each be in the range of from about 0.05 to about 50, preferably from about 0.5 to about 3. The gas hourly space velocity (cc feed gas per cc composition of this invention per hour) can be in the range of from about 0.5 to about 10,000, preferably from about 1 to about 1,000.

The feed gas can be formed in any suitable manner, e.g., by mixing CO, O₂ and optionally other gases such as CO₂, N₂, He and the like, such as in a carbon dioxide laser cavity. Or the feed gas can be an exhaust gas from a combustion engine, or it can be air that is to be inhaled by humans and contains undesirable levels of toxic carbon monoxide, and the like. The feed gas can be contacted in any suitable vessel or apparatus, such as in a laser cavity or in an exhaust pipe of a combustion engine, wherein the feed gas passes over the composition of this invention at the conditions described above. The CO oxidation process of this invention can be carried out in any suitable setting and for any purpose, e.g., for recombining CO and O₂ in CO₂ lasers or, to oxidize CO contained in exhaust gases or air, and the like.

The following examples are presented in further illustration of the invention and are not to be construed as unduly limiting the scope of the invention.

EXAMPLE I

This example illustrates the experimental setup for testing the activity of the composition of this invention for catalyzing the oxidation of carbon monoxide (so as to simulate catalytic recombination of CO and O₂ in CO₂ lasers). A gaseous feed blend comprising CO, O₂, CO₂, He and N₂ was passed through a needle valve and a glass reactor in an upflow direction. The glass reactor tube had an inner diameter of about 6 mm and generally contained about 1.0 gram catalyst in a bed of about 2.5 cm height. The temperature in the catalyst bed was measured by means of a thermocouple inserted into the top layer of the catalyst bed. The CO content in the reactor effluent was determined by means of a Beckman Model 864 IR analyzer.

All tests were carried out at ambient conditions (about 25° C.; 1 atm.). Generally the temperature in the catalyst bed rose to about 30° C. because of the generation of heat during the CO oxidation tests. The feed rate of the gaseous feed stream was about 400 cc/minute. The gaseous feed contained 1.2 volume-% CO, 0.6 volume-% O₂, 32 volume-% He, 32 volume-% CO₂ and N₂ as the balance.

EXAMPLE II

This example illustrates the preparation of various cemented catalyst compositions.

Cemented catalyst Composition A contained 67 weight-% Type III portland cement (manufactured by Lone Star Industries, Tulsa, Okla.) and 33 weight-% of a catalyst consisting essentially of 3 weight-% Pt, 1 weight-% Fe (as iron oxide) and TiO₂ as support material (prepared by impregnation of TiO₂ with Pt and Fe compounds, followed by calcination and reduction with H₂, substantially in accordance with the procedure described in U.S. Pat. No. 4,920,088). Catalyst Composition A was prepared by mixing (with stirring) 16.0 grams of a Type III portland cement, 8.0 grams of the Pt/Fe/TiO₂ catalyst and 12 cc of distilled water. The obtained mixture was kept at room temperature in a hydrostat for about 2 days.

Cemented Catalyst Composition B contained about 65 weight-% Type III portland Cement, 32.5 weight-% of the Pt/Fe/TiO₂ catalyst described above, and 2.5 weight-% of Na silicate. Cemented Catalyst Composition B was prepared by mixing 10 grams of Type III portland cement, 5.0 grams of the Pt/Fe/TiO₂ catalyst, 0.4 grams of Na metasilicate beads (provided by PQ Corporation, Valley Forge, Pa.), and 8.0 grams of distilled water. The mixture was stirred, cast into microtiter plates of 0.5 cm diameter, and kept in a hygrostat at room temeperature for about 2 days.

Cemented Catalyst Composition C contained 65 weight-% Class H well cement, 32.5 weight-% of the Pt/Fe/TiO₂ catalyst described above, 0.4 grams of Na metasilicate beads, and 8.0 grams of distilled water. This composition was prepared in accordance with the procedure for Cemented Catalyst Composition B, except that a Class H well cement (provide by Trinity LaFarge, Montreal, Canada) was used in lieu of Type III portland cement.

EXAMPLE III

This example illustrates the CO oxidation activity of the various cemented catalyst compositions described in Example II. These cemented catalyst compositions were exposed for 2 hours to free hydrogen at 200° C. before they were tested in the CO oxidation reactor. Test results are summarized in Table I.

                  TABLE I                                                          ______________________________________                                         Cemented              Conversion of cc CO                                      Catalyst      Time    per Minute per Gram                                      Composition   (hours) Catalyst                                                 ______________________________________                                         A             1       0.70                                                     (Control)     2       0.67                                                                   4       0.65                                                                   6       0.64                                                                   8       0.63                                                                   10      0.62                                                                   15      0.59                                                                   20      0.56                                                     B             1       1.02                                                     (Invention)   2       0.97                                                                   4       0.90                                                                   6       0.86                                                                   8       0.82                                                                   10      0.79                                                                   15      0.74                                                                   20      0.70                                                     C             1       1.30                                                     (Invention)   2       1.24                                                                   4       1.18                                                                   6       1.14                                                                   8       1.11                                                                   10      1.09                                                                   15      1.02                                                                   20      0.98                                                     ______________________________________                                    

Test data in Table I clearly show that the Na silicate containing cemented compositions B and C were considerably more active as CO oxidation catalysts than cemented composition A without Na silicate. Composition C with Class H well cement was more active than Composition B with Type III portland cement. Additional test data (not included in Table I) indicate that a composition which was essentially the same as Composition C but was prepared in the presence of aluminum metal powder during mixing of the various components and water (so as to generate hydrogen gas) did not consistently perform better than Composition C in the above-described CO oxidation tests.

Reasonable variations, modifications and adaptations for various usages and conditions can be made within the scope of the disclosure and the appended claims, without departing from the scope of this invention. 

That which is claimed is:
 1. A process for preparing a solid composition of matter which comprises a mixture of(1) a hardened hydraulic cement, (2) sodium silicate and (3) a catalyst composition comprising (a) an inorganic support material, (b) at least one of platinum and palladium metal, and (c) at least one iron component selected from the group consisting of iron metal, iron oxide and mixture thereof;said process comprising the steps of: (A) mixing water, a hydraulic cement, sodium silicate and said catalyst composition comprising components (a), (b) and (c), and (B) maintaining the mixture obtained in step (A) under such conditions so as to affect hardening of the hydraulic cement, and to substantially dry the mixture of step (A) so as to obtain a substantially dry, solid composition of matter.
 2. A process in accordance with claim 1, wherein said hydraulic cement is selected from the group consisting of Type III portland cement, Class H well cement and mixtures thereof.
 3. A process in accordance with claim 1, wherein said sodium silicate is sodium metasilicate.
 4. A process in accordance with claim 1, wherein component (a) of said catalyst composition is selected from the group consisting of alumina, magnesia, magnesium aluminate, hydrotalcite, silica, titania, zirconia, vanadia and mixtures thereof.
 5. A process in accordance with claim 1, wherein said catalyst composition comprises titania as support material, platinum metal and iron oxide.
 6. A process in accordance with claim 5, wherein said hydraulic cement is at least one of Type III portland cement and Class H well cement, and said sodium silicate is sodium metasilicate.
 7. A process in accordance with claim 1, wherein in step (A) the weight ratio of said hydraulic cement to said catalyst composition is in the range of about 0.1:1 to about 10:1, the weight ratio of said hydraulic cement to said sodium silicate is in the range of about 2:1 to about 200:1, and the weight ratio of said hydraulic cement to said water is in the range of about 0.1:1 to about 20:1.
 8. A process in accordance with claim 1, wherein in step (A) the weight ratio of said hydraulic cement to said catalyst composition is in the range of about 0.5:1 to about 3:1, the weight ratio of said hydraulic cement to said sodium silicate is in the range of about 10:1 to about 50:1, and the weight ratio of said hydraulic cement to said water is in the range of about 0.5:1 to about 4:1.
 9. A process in accordance with claim 1 comprising the additional step of treating the material obtained in step (B) with free hydrogen at about 100°-300° C.
 10. A solid composition of matter which comprises a mixture of(1) a hardened hydraulic cement, (2) sodium silicate and (3) a catalyst composition comprising (a) an inorganic support material, (b) at least one of platinum and palladium metal, and (c) at least one iron component selected from the group consisting of iron metal, iron oxide and mixtures thereof.
 11. A composition of matter in accordance with claim 10, wherein said hydraulic cement is selected from the group consisting of Type III portland cement and Class H well cement.
 12. A composition of matter in accordance with claim 10, wherein component (a) of said catalyst composition is selected from the group consisting of alumina, magnesia, magnesium aluminate, hydrotalcite, silica, titania, zirconia, vanadia and mixture thereof.
 13. A composition of matter in accordance with claim 10, wherein said catalyst composition comprises titania as support material, platinum metal and iron oxide.
 14. A composition of matter in accordance with claim 13, wherein said catalyst composition comprise 0.05-10 weight-% Pt and about 0.1-15 weight-% Fe.
 15. A composition in accordance with claim 14, wherein said hydraulic cement is at least one of Type III portland cement and Class H well cement, and said sodium silicate is sodium metasilicate.
 16. A composition of matter in accordance with claim 10, being active as a catalyst for oxidizing CO with O₂ to CO₂ at about 10°-50°C.
 17. A composition of matter in accordance with claim 10, having been prepared by a process comprising the steps of:(A) mixing water, a hydraulic cement, sodium silicate, and said catalyst composition comprising components (a), (b) and (c), and (B) maintaining the mixture obtained in step (A) under such conditions so as to affect hardening of the hydraulic cement, and to substantially dry the mixture of step (A) so as to obtain a substantially dry, solid composition of matter.
 18. A composition in accordance with claim 17, wherein said hydraulic cement is at least one of Type III portland cement and Class H well cement.
 19. A composition in accordance with claim 17, wherein said sodium silicate is sodium metasilicate.
 20. A composition in accordance with claim 17, wherein component (a) of said catalyst composition is selected from the group consisting of alumina, magnesia, magnesium aluminate, hydrotalcite, silica, titania, zirconia, vanadia and mixtures thereof.
 21. A composition in accordance with claim 17, wherein said catalyst composition comprises titania as support material, platinum metal and iron oxide.
 22. A composition in accordance with claim 21, wherein said hydraulic cement is at least one of Type III portland cement and Class H well cement, and said sodium silicate is sodium metasilicate.
 23. A composition in accordance with claim 17, wherein in step (A) the weight ratio of said hydraulic cement to said catalyst composition is in the range of about 0.5:1 to about 3:1, the weight ratio of said hydraulic cement to said sodium silicate is in the range of about 10:1 to about 50:1, and the weight ratio of said hydraulic cement to said water is in the range of about 0.5:1 to about 4:1.
 24. A composition in accordance with claim 17, having been treated with free hydrogen at about 100°-300° C. 